88 Bronco ii rough run intermittant and rich

It's one year later and the same problem came up again. My code reader didn't indicate anything wrong so I went to a reliame repair facility. They came up with a code 41 and replaced the o2 sensor. It's running well except for a little stumble when cold just after starting out.
That could be due to the vacuum to the air cleaner being plugged for a leak at the bi-metal device.

i had a simmilar problem with my 88 a few years ago, the shop replaced the sensor and works fine for a few days and then the problem start again and again, after a lot days without success, i went to another shop and they replaced the gas regulator, problem solved until now